1. Field of the Invention
The present invention relates to a depth of field (DOF) control device and in particular, a depth of field (DOF) control device installed on an automatic document feeder (ADF) to achieve a better DOF control.
2. Description of the Prior Art
Referring to FIG. 1 and FIG. 2, office copy machines such as a printer or an image scanner having an automatic document feeder (ADF) are known in the art. Generally, a depth of field or depth of focus (DOF) controller is provided in the automatic document feeder for precisely control the object to be scanned, which is placed across a transparent glass of a scanner or a printer, within an acceptable range of DOF during the scan in order to obtain a clear image on a copy sheet.
FIG. 1 and FIG. 2 illustrate a typical DOF control (0.1˜0.2 mm). A plate member (metal plate) 10a is used. The plate member (metal plate) 10a has a rotation center 11a. Through the rotation center 11a, the plate member (metal plate) 10a is pivotally installed on the automatic document feeder 12a. 
However, the prior art DOF control device is not perfect. When the automatic document feeder 12a and the underlying glass surface 13a cannot provide an even surface, one end of the object to be scanned will attach the glass while the other end will float in the air, causing a sever DOF control problem.
Accordingly, there is a strong need for an improved DOF control device which has good reliability.